Psychology Endogenous Vs Exogenous
Discuss the role of endogenous pacemakers and exogenous zeitgebers in the sleep/wake cycle and one other rhythm (24)
Siffre (1975) dedicated 6 months of his life to be spent isolated in an underground cave in Texas. During which, he was exposed to only artificial light, and was given no natural exogenous zeitgebers. This meant that his biological rhythms were subject to free running, whereby the body has to dictate its own resources and has no external aid, such as natural light or social norms, telling the suprachiasmatic nucleus it is time to rest.
Siffre found that in the absence of such influences, his sleep-wake circadian rhythm extended from the normal 24 hours to between 25 and 36 hours. As a consequence, upon emergence on the 179th day, in Siffre’s terms it was only his 151st day.
From Siffre’s findings, we are able to concur that the endogenous pacemakers are still active during isolation, but become somewhat distorted over time, as the brain’s SCN loses influence from the exogenous zeitgebers and therefore going out of sync by even a minute a day can lead to serious desynchronisation over time.
His body temperature circadian rhythm was more stable. It extended slightly to about 25 hours, but remained consistent. One outcome of this was that Siffre’s sleep-waking cycle became desynchronised from his body temperature rhythm. Under normal conditions they are synchronised, so that we regularly go to sleep when body temperature is falling and awake when it is rising.
The main critique of this study is the fact that it was obviously conducted on one man alone. We cannot guarantee ecological validity of this study as doing so we may fall to evolutionary determinism, whereby it is presumed all of mankind is subject to identical biological patterns.
There are also ethical issues, as although Siffre obviously volunteered to do this experiment, we are inevitably unsure of the reasoning behind such a drastic decision. The martyresque nature of this
Siffre (1975) dedicated 6 months of his life to be spent isolated in an underground cave in Texas. During which, he was exposed to only artificial light, and was given no natural exogenous zeitgebers. This meant that his biological rhythms were subject to free running, whereby the body has to dictate its own resources and has no external aid, such as natural light or social norms, telling the suprachiasmatic nucleus it is time to rest.
Siffre found that in the absence of such influences, his sleep-wake circadian rhythm extended from the normal 24 hours to between 25 and 36 hours. As a consequence, upon emergence on the 179th day, in Siffre’s terms it was only his 151st day.
From Siffre’s findings, we are able to concur that the endogenous pacemakers are still active during isolation, but become somewhat distorted over time, as the brain’s SCN loses influence from the exogenous zeitgebers and therefore going out of sync by even a minute a day can lead to serious desynchronisation over time.
His body temperature circadian rhythm was more stable. It extended slightly to about 25 hours, but remained consistent. One outcome of this was that Siffre’s sleep-waking cycle became desynchronised from his body temperature rhythm. Under normal conditions they are synchronised, so that we regularly go to sleep when body temperature is falling and awake when it is rising.
The main critique of this study is the fact that it was obviously conducted on one man alone. We cannot guarantee ecological validity of this study as doing so we may fall to evolutionary determinism, whereby it is presumed all of mankind is subject to identical biological patterns.
There are also ethical issues, as although Siffre obviously volunteered to do this experiment, we are inevitably unsure of the reasoning behind such a drastic decision. The martyresque nature of this